The scope of the work for this clinical research program, "Therapy of Patients with early Stage Colorectal Cancer" encompasses post-surgical treatment for patients at high risk for recurrence. In rectal cancer this will include treatment for all patients with positive lymph nodes in their surgically resected tumnor specimens. The clinical trial, which builds on previous Gastrointestinal Tumor Study Group data, will randomize patients into one of two treatment arms. Both will include radiotherapy and chemotherapy. Only one arm will include two chemotherapeutic agents, 5-fluorouracil and methyl-CCNU, the other 5-fluorouracil alone in escalating dosage after radiation is completed. The trial in colon cancer includes patients whose tumors push through the colonic serosa or have positive lymph nodes. Only patients with positive lymp nodes will be randomized to a no treatment control arm or a therapy of radiation to the liver (2000 rads) plus 5-fluorouracil at the outset of radiation treatment and for two courses subsequent to the radiation treatment. Patients with serosal penetration, but with negative lymph nodes, will be registered, but not randomized.